Can shale drilling result in a wild well?

11:03 am, July 24, 2012

Editor's note: On July 16, there was a gas well fire in Bolivar, Ohio, resulting in one death. While that well was a conventional gas well and not horizontally fracked, it brings to mind the question of safety with regards to drilling for gas. One of the nation's foremost experts on petroleum engineering, Jim Rike, addresses the question of shale drilling and well safety in this week's column. Mr. Rike is president of Rike Service, an oilfield service company and engineering consulting firm in Tickfaw, La., as well as a visiting professor at Marietta College, where he teaches petroleum engineering.

A wild well is often called a “blowout,” with consequential unrestrained flow at the surface. It often catches fire from a momentary spark. You see scenes on TV of flames engulfing the drilling rig, reaching 100 feet in the air, and smoke erupting as it does from a building fire.

A blowout can occur on any well due to surprise penetration of high-productivity oil- or gas-bearing strata if the crews are not well trained of if they do not react quickly enough. Intense training on this subject is required of specific members of the on-site drilling team, including practice on a “well control simulator.”

All blowouts — or “well kicks,” as we call them it if we prevent the blowout — are preceded by warning signs. Proper training makes all of the crew members sensitive to these signs; supervisory personnel are required to take tests demonstrating their ability to recognize warning signs, as well as how to expeditiously control the well before it becomes a blowout.

One example of a warning sign is noting that more fluid is coming out of the well than is going in. Obvious, isn't it? The crew gets that signal because mud tanks supply the drilling fluid being pumped into the well, and these tanks catch the returning fluid coming back out while drilling. So, a “tank gain” while drilling means extra fluid is coming from down hole. It is a warning sign, because it takes time for that excess flow to reach the surface.

When we see the tank gain start, we close a very large valve on the “blowout preventer” (BOP) that seals around the pipe to prevent flow. We place a check valve inside the top of the drill pipe to keep flow from coming up inside the pipe. Thus the well is contained, inside and outside the drill pipe. The crew initiates a “kill” procedure that circulates heavier fluid to replace the lighter fluid which is heavy enough to hold down the flow.

These procedures are not just learned in a classroom; rules require a test on a simulator that behaves exactly like a real well with the new downhole flow coming in. It is similar to the simulators used to test airplane pilots or car driver reaction time. Essentially, all blowouts can be traced to inadequate attention to warning signs or slow reaction to those signs.

This blowout preventer as well as the crew's reaction ability is regularly tested on the drilling site. The practice tests are not always announced. The device indicating a tank gain can be manipulated to register a gain falsely. This allows management or regulatory personnel to note how quickly the crews respond and complete the well control procedure without announcing it as a practice drill. State regulatory bodies specify the frequency of testing the BOP as well as the degree of training and re-training required of the rig crew and supervisory personnel.

When drilling shale wells as in the Marcellus and Utica formations in Ohio, the geology is now well known and surprise penetrations of potential flowing zones are practically non-existent. Before “fracking,” the shale by itself won't support sustained flow or a blowout. The well has essentially no potential for blowout until stimulated by the first frack job. Any flow before that will be a few bubbles in the drilling fluid, not enough to support flow or cause a catastrophe.

Once the well has been stimulated, it has the potential for a blowout. Any later operation on the well, often referred to as “completion” or a “well intervention” or “workover,” has the potential for a blowout.

The lack of blowouts or wild wells is indicative of good prevention equipment, regularly tested to demonstrate its effectiveness against the highest pressure anticipated. It is also a reflection of good training and regular practice by the drilling rig crews as well as all personnel engaged in subsequent well interventions.

Jim Rike is president of Rike Service, an oilfield service company and engineering consulting firm in Tickfaw, La., as well as a visiting professor at Marietta College, where he teaches petroleum engineering.